1. Coulomb’s Law p. 538 in your book

2. Charged objects & electrical force Two electrically charged objects exert a force on each other. Opposite charges ATTRACT Notice the forces are “equal but opposite”

3. Charged objects & electrical force Two electrically charged objects exert a force on each other. Like charges REPEL Notice the forces are “equal but opposite”

4. Coulomb’s Law

6. Example 1 p. 539 Two objects, whose charges are +1.0C and -1.0C are separated by 1.0km. Find the magnitude of the attractive force that either charge exerts on the other. F = 9.0x10 3 N

7. Notice anything familiar? Similarities: Both are inverse square laws The force is directed along a line between the two objects Difference: Electrostatic force can be either attractive or repulsive Gravitational force is always attractive

8. Notice anything familiar?

9. More than 2 point charges We can use Coulomb’s law to determine the net electrostatic force acting on a point charge (q 1 ) due to multiple other point charges (q 2 and q 3 ).

10. More than 2 point charges First determine the force (magnitude and direction!) that q 3 exerts on q 1 (ignore q 2 ) Then determine the force (magnitude and direction!) that q 2 exerts on q 1 (ignore q 3 )

11. More than 2 point charges The net force on q1 is the vector sum of these two forces.

12. Example 4 p. 541 Determine the magnitude and direction of the net electrostatic force on q 1. +5.7N

13. Assignment Coulomb’s law worksheet